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1.
Unconventional antiferromagnetic correlations of the doped Haldane gapsystem Y 2 BaNi 1 - x Zn x O 5
V. Villar R. Mélin C. Paulsen J. Souletie E. Janod C. Payen 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(1):39-51
We make a new proposal to describe the very low temperature susceptibility of the doped Haldane gap compound Y2BaNi1-xZnxO5. We propose a new mean field model relevant for this compound. The ground state of this mean field model is unconventional
because antiferromagnetism coexists with random dimers. We present new susceptibility experiments at very low temperature.
We obtain a Curie-Weiss susceptibility χ(
T
) ∼
C
/(Θ +
T
) as expected for antiferromagnetic correlations but we do not obtain a direct signature of antiferromagnetic long range order.
We explain how to obtain the “impurity” susceptibility
(
T
) by subtracting the Haldane gap contribution to the total susceptibility. In the temperature range [1 K, 300 K] the experimental
data are well fitted by T
(
T
) =
C
imp
1 +
T
imp
/
T
. In the temperature range [100 mK, 1 K] the experimental data are well fitted by T
(
T
) =
A
ln(
T
/
T
c
), where T
c
increases with x. This fit suggests the existence of a finite Néel temperature which is however too small to be probed directly in our experiments.
We also obtain a maximum in the temperature dependence of the ac-susceptibility
(
T
) which suggests the existence of antiferromagnetic correlations at very low temperature.
Received 17 July 2001 相似文献
2.
Travert A Nakamura H van Santen RA Cristol S Paul JF Payen E 《Journal of the American Chemical Society》2002,124(24):7084-7095
Hydrogen adsorption on Mo[bond]S, Co[bond]Mo[bond]S, and Ni[bond]Mo[bond]S (10 1 macro 0) surfaces has been modeled by means of periodic DFT calculations taking into account the gaseous surrounding of these catalysts in working conditions. On the stable Mo[bond]S surface, only six-fold coordinated Mo cations are present, whereas substitution by Co or Ni leads to the creation of stable coordinatively unsaturated sites. On the stable MoS(2) surface, hydrogen dissociation is always endothermic and presents a high activation barrier. On Co[bond]Mo[bond]S surfaces, the ability to dissociate H(2) depends on the nature of the metal atom and the sulfur coordination environment. As an adsorption center, Co strongly favors molecular hydrogen activation as compared to the Mo atoms. Co also increases the ability of its sulfur atom ligands to bind hydrogen. Investigation of surface acidity using ammonia as a probe molecule confirms the crucial role of sulfur basicity on hydrogen activation on these surfaces. As a result, Co[bond]Mo[bond]S surfaces present Co[bond]S sites for which the dissociation of hydrogen is exothermic and weakly activated. On Ni[bond]Mo[bond]S surfaces, Ni[bond]S pairs are not stable and do not provide for an efficient way for hydrogen activation. These theoretical results are in good agreement with recent experimental studies of H(2)[bond]D(2) exchange reactions. 相似文献
3.
The compounds P2O3F4 and K2P2O5F2 have been studied by vibrational spectroscopy. From the shifts of the symmetric vibration of the terminal PO bonds it appears that the molecular structure contracts as the number of PO (bridged) and/or PF bonds increases. The changes occur at the expense of PO terminal bonds. In these tetrahedral phosphorus (V) compounds the PO (bridged) and PF bonding have a similar role, and the same phenomenon occurs in sulfur VI oxide fluoride compounds. 相似文献
4.
Delphine Catel Olivier Payen Floris Chevallier Florence Mongin Philippe C. Gros 《Tetrahedron》2012,68(21):4018-4028
Butyl and dibutylmagnesiates incorporating chiral ligands have been prepared and their reactivity studied. The reagents were efficient to promote the clean bromine–magnesium exchange of azinyl bromides at room temperature and subsequent reaction with aldehydes affording pyridylcarbinols. (R,R)-TADDOL-based dibutylmagnesiate was the best reagent leading to acceptable to good enantioselectivities, depending on the substrate and on the aldehyde substitution. This is the first example of enantioselective addition of in situ generated pyridylmagnesiate to carbonyl electrophiles. 相似文献
5.
Comparison of Drying Procedures for the Preparation of Alumina Powders with the System Al-Alkoxide/Tertiary Butanol/Water 总被引:1,自引:0,他引:1
E. Ponthieu E. Payen G.M. Pajonk J. Grimblot 《Journal of Sol-Gel Science and Technology》1997,8(1-3):201-206
Two series of alumina gel precursors, obtained from Al sec-butylate, ASB, or Al tert-butylate, ATB, dissolved in tertiary
butanol, TB, have been dried according to five procedures, in order to compare their efficiency and the consequences they
may have on the structure of the final product. They consist of lyophilization (or freezedrying), evacuation at room temperature
(with or without ageing of the gel), drying in an oven at atmospheric pressure, or under hypercritical conditions. Chemical
analysis, X-Ray diffraction and spectroscopic characterizations (FTIR and laser Raman) allow the identification of the phases
present. The temperature of the drying step, as well as the nature of the alkoxide percursor, considerably affect the final
dried products. 相似文献
6.
Payen 《Fresenius' Journal of Analytical Chemistry》1865,4(1):490-491
Ohne Zusammenfassung 相似文献
7.
A formula at low temperature for the function G() = Iλλ6 has been derived in terms of configuration curve theory and checked on luminescence spectra near 77 K. The vibrational quantum in the excited state has been calculated from the decrease of G(), where λM is the wavelength of the maxima of G at low temperature, as a function of temperature. 相似文献
8.
Laser Raman Spectroscopy is used to study catalysts : Co, Mo or Co-Mo supported on alumina. Well defined salts spectra are compared to those of these solids, which permits to establish superficial structures of cobalt, molybdenum or both. For molybdenum catalysts, we found two structures depending upon the concentration isolated MoO2- 4 molecular ions at low concentration < 4% polymolybdate phase at higher concentration For cobalt catalysts two structures are also observed: - tetrahedrally surrounded co 2+ ions at low concentration Co3O4 clusters at higher concentrations For cobalt-molybdenum (8%) catalysts three cases occur no effect is observable at very low concentration of cobalt (0.5%) a well defined compound appears for Co/Mo atomic ratio 0.25 when the cobalt concentration increases a third structure is observed but not identified All these results are compared to X Ray photoelectron spectroscopic studies and are in good agreement with them. 相似文献
9.
Quantification of β‐aminopropionitrile,an inhibitor of lysyl oxidase activity,in plasma and tumor of mice by liquid chromatography tandem mass spectrometry
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Christelle Machon Benjamin Le Calve Sylvie Coste Mirella Riviere Léa Payen David Bernard Jérôme Guitton 《Biomedical chromatography : BMC》2014,28(7):1017-1023
Lysyl oxidase enzymes are reported to be involved in patho‐physiological process such as tumorigenesis. β‐Aminopropionitrile (BAPN) is an irreversible inhibitor of lysyl oxidase activity, suggesting a potentially useful therapeutic of interest in oncology. This paper describes the first assay concerning the quantification of BAPN by mass spectrometry. A high‐performance liquid chromatography tandem mass spectrometry (LC‐MS/MS) assay was developed for the quantification of BAPN in plasma and tumor of mice. This method combines dansyl chloride (Dns) derivatization and extraction using a solid‐phase extraction Oasis© Max column. Deuterated BAPN was used as internal standard (IS). Separation was achieved using an C18 column HypersylGold, (ThermoElectron), 3.0 µm (100 × 2.1 mm i.d.). Gradient elution with water containing 0.1% acetic acid (A) and acetonitrile containing 0.1% acetic acid (B) was applied. Detection was performed with an electrospray ionization interface operating in negative ion mode. Selected reaction monitoring was used with ion transitions m/z 302 → 249 for BAPN–Dns and m/z 306 → 250 for the IS. The method was fully validated in plasma and was linear and sensitive in the range of 10–500 ng/mL. The lower limit of quantification in plasma was 2.5 ng/mL. This validated assay was successfully applied to a kinetic study of BAPN in mouse plasma and demonstrates that BAPN reaches the tumoral tissue. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
10.
N. De Geyter R. Morent L. Gengembre C. Leys E. Payen S. Van Vlierberghe E. Schacht 《Plasma Chemistry and Plasma Processing》2008,28(2):289-298
Plasma surface modification is widely used to tailor the surface properties of polymeric materials. Most treatments are performed
using low pressure plasma systems, but recently, atmospheric dielectric barrier discharges (DBDs) have appeared as interesting
alternatives. Therefore, in this paper, an atmospheric He + CF4 DBD is used to increase the hydrophobicity of a polypropylene (PP) film. The surface characterization of the PP film is performed
using contact angle measurements, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Results show that
the hydrophobic properties of the polymer films are greatly enhanced after plasma treatment as evidenced by an increased contact
angle. The incorporation of fluorine on the surface is significant (45 at%), demonstrating the ability of the used DBD set-up
to generate fluorine-containing functional groups on the PP surface. 相似文献